逆康普顿散射对γ暴余辉的影响

γ暴余辉的发现是γ暴研究史上的一个重大突破,火球模型几乎可以较好地解释γ暴余辉的观测特性。但在标准的火球模型中,通常只考虑电子的同步加速辐射,没有考虑电子逆康普顿散射的贡献。这里我们详细计算了逆康普顿散射对γ暴余辉的影响,发现在一定的条件下,逆康普顿散射的影响是很重要的,它可以显著地改变辐射能谱,进而改变γ暴余辉的光变特性。     

强磁场中相对论电子系集体的共振逆康普顿散射谱

强磁场中相对论电子的共振逆康普顿散射(RICS)是产生伽玛射线的有效机制.以前的工作曾论证,伽玛暴(GRB)的早期伽玛射线辐射可能主要由该机制产生.利用此辐射机制,伽玛暴研究中的一些困惑有可能得到较好的解释.例如,观测统计给出的"Amati关系"的起源,两段式(折断式)幂律谱的形成,特别是其中"死线问题"的解决方案,还有偏振的存在等.这里将重点讨论折断幂律谱形成问题.基于单个电子的RICS谱功率公式,导出了强磁场中大量相对论电子穿过周边低频辐射场时产生的集体RICS辐射谱(RICS谱光度)的简化解析公式,并将它应用于中子星周边几种典型的低频场(如黑体辐射场、幂律辐射场以及热轫致辐射场),以便与实际观测谱形比较.计算表明:在满足匹配条件(即近似共振条件)下,RICS辐射效率很高,其谱形普遍为两段式的幂律谱形式,与周边低频场性质无关.还论证RICS机制可能是伽玛暴、软伽玛重复暴和伽玛射线脉冲星在高能射线波段(硬X射线和伽玛射线)的一个理想的高效辐射机制.     

磁星能量注入模型拟合伽玛射线暴X射线余辉光变曲线

某些伽玛射线暴(简称伽玛暴)的中心致密天体可能是一颗具有强磁场的毫秒脉冲星,它通过磁偶极辐射可对伽玛暴外激波注入能量,从而导致早期余辉光变曲线的变平.近年来,从Swift卫星观测到的大量伽玛暴X射线余辉中发现,很多X射线余辉光变曲线在暴后10~2～10~4s期间的确存在明显的变平现象.利用周期为毫秒量级的磁星能量注入模型对11个加玛暴的X射线余辉光变曲线进行了拟合,显示该模型在解释余辉变平现象上的有效性和广泛性,通过对余辉光变曲线的拟合,同时也给出了相关中心磁星的磁场强度和旋转周期.     

Swift时代伽玛射线暴及其余辉的多波段研究

<正>伽玛射线暴(简称伽玛暴)是一种来自太空任意方向的伽玛射线(ε_γ≈0.1～1 MeV)脉冲式辐射现象,暴后一般伴随有长时间的低频余辉辐射.为了对早期余辉乃至瞬时辐射进行多波段观测,美国国家航空航天局(NASA)于2004年11月发射了专门用于伽玛暴研究的Swift卫星.该卫星工作以来,以其快速响应与精确定位的能力和多波段观测的手段取得了一系列令人瞩目的成就(本文第1章将对     

致密介质中柱状喷流的伽玛射线暴余辉

很多伽玛射线暴应当是产生于极端相对论性的喷流.关于喷流,绝大多数的讨论都是围绕锥状喷流展开.然而有观测发现,一些天体中的喷流在很长距离上始终保持着几乎不变的截面积,即表现为柱状喷流.研究致密介质环境中有侧向膨胀的柱状喷流的余辉,描述其动力学演化和辐射过程,分别得到解析解和数值解,并对两者进行了对比.研究的暴周星际介质是光学厚的,在初始的主暴阶段,喷流辐射出高度准直的高能射线,升华了暴周介质,形成一个在光学波段光学薄的柱状通道.余辉阶段,由于喷流是有侧向膨胀的,观测者只能收集到视觉面积占比例越来越小的光学辐射,理论上可得到衰减极为快速的光变曲线,流量随时间的衰减约为Svα t-p-1(p为电子幂律分布的谱指数).如此迅速的衰减使得光学余辉将难以被观测到,提供了一种对暗伽玛射线暴的解释.     

共动系中伽玛暴峰值能量的分布及其与光度的关系

伽玛暴νfν谱的峰值能量E_p是伽玛暴的一个很重要的观测物理量,观测系中伽玛暴νf_ν谱的峰值能量Ep分布很宽.根据各向同性光度L_(iso)、初始洛伦兹因子Γ_0和暴源系中峰值能量E_p,z之间的关系式估算伽玛暴的初始洛伦兹因子Γ_0,再把伽玛暴νf_ν谱的峰值能量E_p和光度L_(iso)修正到共动坐标系,发现共动系中峰值能量的分布还是很宽.这意味着观测系中E_p的宽分布可能是伽玛暴的真实物理分布.检验了共动坐标系中光度和峰值能量之间的关系,发现它们之间仍然存在相关性.最后,进一步对伽玛暴的辐射物理进行限制,认为共动坐标系中峰值能量分布很宽可能是由于辐射电子的洛伦兹因子γ_e分布很宽.     

伽玛射线暴及其余辉研究进展

伽玛射线暴是一种来自宇宙空间随机方向的短时间内伽玛射线突然增亮的现象。伽玛射线暴虽然早在1967年就由Vela卫星观测到,但直到1997年人们才通过余辉观测确定其寄主星系,并通过寄主星系的红移最终确定了伽玛射线暴的宇宙学起源。对伽玛射线暴研究概况进行了评述:详细介绍了伽玛射线暴及其余辉的观测进展,特别是近期Swift卫星和Fermi卫星带来的新发现;系统描述了伽玛射线暴标准火球模型、伽玛射线暴余辉物理(相对论性外流与暴周环境介质的相互作用过程、辐射产生机制等)及伽玛射线暴的前身星等。也对伽玛射线暴的未来研究进行了展望。     

伽玛射线暴:各向同性火球还是柱形喷流?

多数伽玛射线暴的光学余辉衰减较平缓且光变曲线未见明显拐折，通常认为它们产生于各向同性火球，GRBs970228,970508,971214,980329及980703等就是典型的例子，但柱型喷流模型其实也能对这类伽玛射线暴的余辉给出极好的拟合，因此它们完全有可能产生于柱形喷流，而并非一定是来自各向同性火球。     

伽玛暴宇宙学的研究

伽玛射线暴(简称伽玛暴,gamma-ray burst (GRB))是一种来自宇宙空间中的伽玛射线波段流量突然增亮的现象,最早由Vela卫星在1967年发现.1997年人们通过余辉测得了伽玛暴的红移,从而确定了其宇宙学的起源.伽玛暴宇宙学包括用长暴的标准烛光关系限制暗能量和宇宙学参数,用长暴研究高红移的恒星形成率,研究金属丰度的演化、尘埃及量子引力等.     

共动坐标系中伽玛暴νF_ν谱的峰值能量分布

伽玛暴能谱νF_ν的峰值能量Ep是伽玛暴一个很重要的观测物理量,各种仪器观测的伽玛暴νF_ν谱的峰值能量Ep分布都很宽。根据初始洛伦兹因子Γ0,把伽玛暴νF_ν谱的峰值能量Ep修正到共动坐标系,发现Ep在不同坐标系中分布的宽窄程度没有显著差别,说明观测的峰值能量Ep分布比较宽应该不是多普勒放大作用,可能是伽玛暴峰值能量Ep的真实分布。     

Analytical Afterglow Light Curves of Gamma-ray Bursts: the Case of a Flat Electron Spectrum

In the standard afterglow model, the swept electrons have a single power-law energy distribution dn/dγe ∝ γ−p e (p ∼ 2.3), owing to the first order Fermi acceleration process. However, in some events people find a lot of evidence for a flat electron spectrum (i.e., p < 2). In this work, the analytical afterglow light curves in the case of a flat electron energy distribution are presented respectively for a single power-law spectrum and a broken power-law spectrum, then the results are applied to the specific burst GRB 060908. Besides, we have also speculated a possible solution of the so-called low energy spectrum crisis of Gamma-ray Bursts     

High-energy afterglow emission from giant flares of soft gamma-ray repeaters: the case of the 2004 December 27 event from SGR 1806–20

We discuss the high-energy afterglow emission (including high-energy photons, neutrinos and cosmic rays) following the 2004 December 27 giant flare from the soft gamma-ray repeater (SGR) 1806−20. If the initial outflow is relativistic with a bulk Lorentz factor  Γ₀∼  tens, the high-energy tail of the synchrotron emission from electrons in the forward shock region gives rise to a prominent sub-GeV emission, if the electron spectrum is hard enough and if the initial Lorentz factor is high enough. This signal could serve as a diagnosis of the initial Lorentz factor of the giant flare outflow. This component is potentially detectable by the Gamma-Ray Large Area Telescope ( GLAST ) if a similar giant flare occurs in the GLAST era. With the available 10-MeV data, we constrain that  Γ₀ < 50  if the electron distribution is a single power law. For a broken power-law distribution of electrons, a higher Γ₀ is allowed. At energies higher than 1 GeV, the flux is lower because of a high-energy cut-off of the synchrotron emission component. The synchrotron self-Compton emission component and the inverse Compton scattering component off the photons in the giant flare oscillation tail are also considered, but they are found not significant given a moderate Γ₀ (e.g. ≤ 10). The forward shock also accelerates cosmic rays to the maximum energy 10¹⁷ eV, and generates neutrinos with a typical energy 10¹⁴ eV through photomeson interaction with the X-ray tail photons. However, they are too weak to be detectable.     

Origin of power-law X-ray emission in the steep power-law state of X-ray binaries

We present a new explanation for the origin of the steep power-law(SPL) state of X-ray binaries.The power-law component of X-ray emission is the synchrotron radiation of relativistic electrons in highly magnetized compact spots orbiting near the inner stable circular orbit of a black hole.It has a hard spectrum that extends to above MeV energies,which is determined by the electron acceleration rate.These photons are then down-scattered by the surrounding plasma to form an observed steep spectrum.We discuss ...     

A Study of the Low Energy Cutoff of Nonthermal Electrons in RHESSI Flares

The flattening at the low energy end of the hard X-ray (HXR) photon spectrum of solar flares was generally thought to be due to a cutoff of nonthermal electrons in flares. However, some authors have suggested that inverse Compton scattering (i.e., the albedo effect) or certain other reaction of flare photons with the lower atmosphere can also lead to the flattening. This paper adopts the method of deriving the cutoff proposed by Gan et al. ^[12–14], and makes a statistical analysis on 100 flares observed by the satellite Ramaty High Energy Solar Spectroscopy Imager (RHESSI) in 2002–2005. We found that after the albedo correction, the HXR photon spectra of 18 flares can be fitted with single powerlaw spectra, and those of 80 flares, with double power-law spectra. Besides, 21 flares can be directly interpreted with a single power-law electron spectrum plus a low energy cutoff. The range of the low energy cutoff is 20–50 keV and the mean value is approximately 30 keV. Some other possible interpretations are also investigated.     

Multiple compton scattering of electrons in a photon field

Consideration is given to the motion of electrons in a photon field of the monoenergetic or power-law spectrum under the conditions when the main mechanism of energy loss is the inverse Compton scattering by field photons. This process changes the primary spectrum of electrons and converts low-energy field photons to high-energy gamma-quanta for which the electron confinement region is assumed to be optically thin. The electron and gamma-ray spectra have been obtained in a wide energy interval including the Klein-Nishina and Thomson regions. A simple qualitative dependence of the solutions found on the field parameters and the primary spectrum of electrons has been established.The electron and gamma-ray spectra have been obtained by numerically solving the kinetic equation dependent on two variables: the energy of electrons and their path (or the time of motion) in a photon field. The results dramatically differ from the solution of the steady-state kinetic equation which depends only on the electron energy and is frequently used in the given problem.     

On the reconciliation of simultaneous microwave imaging and hard X-ray observations of a solar flare

We have compared microwave imaging data for a small flare with simultaneous hard X-ray spectral observations. The X-ray data suggest that the power-law index of the energy distribution of the radiating electrons is 5.3 (thick-target) which differs significantly from the estimate ( = 1.4) from a homogeneous optically-thin gyrosynchrotron model which fits the radio observations well. In order to reconcile these results, we explore a number of options. We investigate a double power-law energy spectrum for the energetic electrons in the flare, as assumed by other authors: the power law is steep at low energies and much flatter at the higher energies which produce the bulk of the microwaves. The deduced break energy is about 230 keV if we tentatively ignore the X-ray emission from the radio-emitting electrons: however, the emission of soft photons by the flat tail strongly contributes to the observed hard X-ray range and would flatten the spectrum there. A thin-target model for the X-ray emission is also inconsistent with radio data. An inhomogeneous gyrosynchrotron model with a number of free parameters and containing an electron distribution given by the thick-target X-ray model could be made to fit the radio data.     

Ring-Shaped Jets in Gamma-Ray Bursts

When the axis of a gamma-ray burst (GRB) does not coincide with the spin axis of its source, there may result a ring-shaped jet. Using some refined jet dynamics, we calculate multi-wavelength afterglow light curves for such ring-shaped jets. In the R-band we find an obvious break in the afterglow light curve due to the beaming effect and the break is affected by many parameters, such as the electron energy fraction ξe, the magnetic energy fraction ξ2B, the width of ring A0 and the medium number density n. The overall light curve can be divided into three power-law stages, I.e., an ultra-relativistic stage, an after-break stage and a deep Newtonian stage. For each stage the power-law index is larger in the ring-shaped jet than in the corresponding conical jet.     

Formation of power-law electron spectra in collapsing magnetic traps

The energy distribution of the fast electrons captured into a collapsing magnetic trap in the solar corona is calculated as a function of the trap length and diameter. It is shown that if the electrons injected into the trap have a power-law spectrum, then their spectrum remains a power-law one with the same slope throughout the acceleration process for both the Fermi and betatron acceleration mechanisms. For electrons with a thermal injection spectrum, the model predicts two types of hard X-ray sources, thermal and nonthermal. Thermal sources are formed in traps dominated by the betatron mechanism. Nonthermal sources with a power-law spectrum are formed when electrons are accelerated by the Fermi mechanism.     

Acceleration of Electrons and Protons in Reconnecting Current Sheets Including Single or Multiple X-points

Kinematic characteristics of electrons and protons in the magnetic reconnecting current sheet in the presence of a guide field are investigated. Particle trajectories are calculated for different values of the guide field by a test-particle calculation. The relationship between the final energy and the initial position has also been studied. We found that the addition of a guide field not only allows particles to get more energy and not only results in the separation of electrons and protons, but also causes the reconnecting electric field to selectively accelerate electrons and protons for different initial positions. The energy spectrum eventually obtained is the common power-law spectrum, and as the guide field increases, the index for the spectrum of electrons decreases rapidly. However, for a weak background magnetic field, proton spectra are not very sensitive to the guide field; but for a strong background field, the dependence of the spectrum index is similar to the electron spectrum. Meanwhile, kinematic characteristics of the accelerated particles in the current sheet including multiple X-points and O-points were also investigated. The result indicates that the existence of the multiple X- and O-points helps particles trapped in the accelerating region to gain more energy, and yields the double or multiple power-law feature.     

Deeply Penetrating Banded Zonal Flows in the Solar Convection Zone

We discuss the spectrum arising from synchrotron emission by fast cooling (FC) electrons, when fresh electrons are continually accelerated by a strong blast wave, into a power-law distribution of energies. The FC spectrum has so far been described by four power-law segments divided by three break frequencies nusa相似文献